Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2016

Assets Measured at Fair Value on a Recurring Basis

The following tables present the major security types we held at September 30, 2016 and December 31, 2015 that are regularly measured and carried at fair value. The tables segregate each security type by the level within the fair value hierarchy of the valuation techniques we utilized to determine the respective securities’ fair value (in thousands):

	At September 30, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	60,146	$	60,146	$	—
Corporate debt securities (2)		413,561		—		413,561
Debt securities issued by U.S. government agencies (2)		63,350		—		63,350
Debt securities issued by the U.S. Treasury (3)		28,025		28,025		—
Debt securities issued by states of the U.S. and political subdivisions of the states (4)		115,781		—		115,781
Investment in Regulus Therapeutics Inc.		9,382		9,382		—
Total	$	690,245	$	97,553	$	592,692

	At December 31, 2015		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	88,902	$	88,902	$	—
Corporate debt securities (2)		438,426		—		438,426
Debt securities issued by U.S. government agencies (2)		89,253		—		89,253
Debt securities issued by the U.S. Treasury (2)		2,601		2,601		—
Debt securities issued by states of the U.S. and political subdivisions of the states (4)		127,656		—		127,656
Investment in Regulus Therapeutics Inc.		24,792		24,792		—
Total	$	771,630	$	116,295	$	655,335

(1)

Included in cash and cash equivalents on our condensed consolidated balance sheet.

(2)

Included in short-term investments on our condensed consolidated balance sheet.

(3)

At September 30, 2016, $6.0 million was included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.

(4)

At September 30, 2016 and December 31, 2015, $11.1 million and $7.5 million, respectively, were included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.